Examining the Trolley Problem Through the Doctrine of the Double Effect (DDE)

Note: This post explores the doctrine of the double effect and its application to the trolley problem moral dilemma. It specifically references Phillipa Foot’s “The Problem of Abortion and the Doctrine of the Double Effect” essay. My understanding is not substantive by any means, so feel free to let me know if I have missed out on something important or misrepresented anything in this post.

Link to Phillipa Foot’s essay: https://​​philpapers.org/​​archive/​​FOOTPO-2.pdf


The trolley problem is one of moral philosophy’s most significant thought experiments that allows us to examine what drives our decisions and how we act in a morally challenging environment. When we are presented with difficult options, what do we choose? And some may say more importantly, why do we choose what we choose?

Initially, the trolley problem was devised by the British philosopher Phillipa Foot in 1967 as a way to examine our decision-making, prioritization in complex situations, values, and the ethical dimension of such. The trolley problem was first introduced in Foot’s essay titled “The Problem of Abortion and the Doctrine of the Double Effect”. This essay discussed the permissibility of certain actions, and to what extent are actions considered to be morally acceptable, using the doctrine of the double effect (DDE). While the DDE was originally credited to St. Thomas Aquinas, as a part of Christian ethics, Foot’s essay applied the doctrine in the context of the trolley problem.

The essay discussed how in some cases, decisions can be very straightforward because intuition is the driving force that guides us. For example, in the case of a natural disaster, it would be morally acceptable to save those in immediate and urgent danger even if it means neglecting those in more trivial and less urgent danger. On the contrary, it may not be considered morally acceptable to deliberately harm a small group of people for the purpose of freeing up more resources for a larger amount of people to use. In these cases, our intuition helps us make the decisions as it is usually quite clear to us on what is right, and what is wrong. However, for times in which decisions are not as straightforward and cannot be made through the sole reliance on our strong intuitions, the DDE can be used as a principle for deciding how to act.

The Doctrine of the Double Effect (DDE)

The prime question that the DDE aims to address is what actions we may or may not take when the interests of human beings conflict with each other.

The DDE essentially makes a distinction between two types of our actions: those that have intended consequences, and those that have unintended consequences. In the latter case, these actions may have foreseen consequences and therefore you may know and understand what the repercussions of a certain action are, but nonetheless, the consequences can be unintended. This can also be considered as a “side effect” of the action rather than its deliberate outcome. Both these action types can be classified as direct and oblique intention, indicating the actions where the agent intended the consequences and those where the agent had foreseen yet unintended the consequences respectively.

Conditions of the DDE

Often, the DDE plays a role when there is a dilemma between allowing harm to some individuals to save others. To determine whether the harm is morally justifiable, four conditions of the DDE must be satisfied:

  1. The action itself must be morally good, or at least ethically neutral

  2. The person doing the action does not will/​ intend the harm

  3. The good outcome must be caused by the action, not the harm

  4. The good end must be justified in proportion to the harm

The doctrine can therefore be applied to determine whether it is permissible to pursue an action to achieve a morally permissible outcome even if the action will also lead to “bad” results. For instance, the DDE’s application can be examined in the well-known trolly problem thought experiment.

Application of the DDE to the Trolley Problem

In this hypothetical scenario, consider yourself seated on a trolley cart on a train track. Ahead of you, positioned directly on the same track, are five workers. The trolley, if left on its current course, will inevitably result in the death of these five individuals. However, there’s an option to divert the same trolley cart to an alternative track by pulling a lever inside the trolley. On this alternative track, only one worker is present. By pulling the lever, the trolley will be redirected leading to the death of the one worker instead of the five on the original track.

A few assumptions that are kept in this thought experiment to force the moral choice between only two options are that you cannot stop the trolley, the workers are not able to move out of the train track, and no one can anyone interfere and make a decision for you. Hence, the thought experiment forces us to make a decision between what to do, and as a result, poses questions on why we chose to do what we did.

The DDE reasons how and when to allow harm in a moral situation by defining our actions as those with intended consequences and those with foreseen yet unintended consequences.

In the trolley problem, two choices can be made; to either pull the lever or not interfere and not pull the lever. If an agent decided to pull the lever, they would have saved the lives of five workers while resulting in harm to one worker. According to the four conditions of the DDE, the first one is satisfied because the action done was simply pulling the lever, which in itself is morally neutral. Secondly, the person doing the action may not have intended the harm if the objective was to solely save the five workers. In this case, the intention was not to deliberately kill the one worker on the alternate track, but instead, it was an unintended consequence or “side effect” of pulling the lever. Although the agent may have understood the consequences and thus foreseen it, it was nonetheless unintended. Thirdly, the good outcome of saving the five lives is directly caused by the pulling of the lever (the action) instead of the harm caused. In fact, there is no correlation between the harm caused and the good outcome because regardless of whether there was a worker on the alternate track or not, the pulling of the lever saves the five workers. Lastly, as saving five lives can be justified in proportion to the death of one worker, the fourth condition is also considered to be satisfied.

On the contrary, by choosing to not divert the trolley, the agent is choosing to not intervene in the situation. Following the first condition of the DDE, the action of not pulling a lever can be considered morally neutral when the action is solely examined. Secondly, the person doing the action of not pulling the lever may not have intended to cause any harm to the five workers but instead could have chosen this to avoid actively and deliberately harming the one worker. Thirdly, the outcome of the one worker’s life being saved is a result of not pulling the lever and hence is not caused by the death of the five workers by any means. Lastly, in the consideration of the proportionality factor, the death of the five workers could be considered disproportionate to saving the one life of the worker. Therefore, since all four conditions have not been met, according to the doctrine, the action of not choosing to intervene by pulling the lever could be considered as morally impermissible.

Limitations of DDE

However, to gain a comprehensive understanding of DDE and its application in the trolley problem thought experiment, it is important to consider the illogicalities and limitations that the DDE poses.

Firstly, despite the distinction of moral actions made by the DDE, it may not be able to provide a strong argument in certain cases. Due to the DDE’s reliance on the intentions of people as a guiding factor on whether an act is morally permissible or not, it can be challenging to differentiate between what consequences are intended, and what are foreseen but unintended consequences.

For example, imagine there is a terminally ill patient enduring excruciating pain. A nurse administrates medication to the patient with the intention of alleviating the patient’s suffering. However, a potential unintended consequence, that was foreseen by the nurse, could be the acceleration of the patient’s death due to the side effects of the medication. In this case, distinguishing between the intention to relieve pain and the unintended consequence of hastening death reiterates the potential limitation in the DDE. Thus, it can be challenging to draw the line between what consequences are intended, and what are foreseen but unintended.

Moreover, the overall essence of the DDE may not always seem logical. There could be situations in which it does not make sense to classify actions as moral or immoral solely based on intentions. For instance, a key example discussed and emphasized in the essay was the application of DDE in the context of abortion. Medically, there are different methods of abortion—some involve directly intending to save the mother, even if it results in the child’s death, while others prioritize saving the mother without intentionally intending harm to the child. Ultimately, despite the method, there is the inevitable death of the baby.

According to the DDE, the classification of whether the medical method was morally permissible or not depends on the intentions of the method and whether the death of the child was intended or not.

However, when you think about it, regardless of the method and its intention, the outcome of the child’s death remains constant. Thus, the question arises on how one of the methods can be considered as moral and the other as not when at the end of the day, directly intending to kill the child and killing the child as an unintended consequence of a method yields the same result. How can we distinguish actions that have the same end as morally permissible or not permissible?

Oblique Intentions

Furthermore, as mentioned earlier—direct and oblique intentions are a way of classifying our actions as those that we do (intended) and those that we allow (foreseen and unintended). Particularly in the context of what we allow to happen, but do not intend (oblique intention), there are still nuances and discrepancies with what “allow” really entails.

On one hand, omission is a type of allowing where there is an absence of action taking place or an absence of any form of interference. On the other hand, commission is when you are actively causing something to occur through the removal of any obstacles that hence lead to an outcome to occur. It may seem obvious that omission correlates to a morally permissible action because you are simply not interfering rather than causing something to occur, while commission can be considered the opposite because of deliberately interfering and actively causing something to occur. However, the essay discusses cases in which both omission and commission are considered equally bad. For example, according to the essay, a man may murder his child by allowing them to die from starvation or by giving them poison, both of which are reasons for him to be convicted of murder. There are other cases though in which omission is not nearly as bad as commission. How can we compare allowing people to die of starvation in underprivileged countries to deliberately sending them poisoned food? Visibly, the main challenge is that it becomes hard to solely assign one type of allowance with the idea of being moral, and the distinction between omission and commission blurs in certain cases.